EPSRC CDT in Metamaterials (PhD Studentship): Optically Induced Magnetization Dynamics of Magnetic Exchange Spring Metamaterials

University of Exeter - Departments of Physics and Engineering

Joint supervisors: Prof Robert J Hicken, Prof Gino Hrkac, Dr Maciej K Dabrowski

Industry partner: Seagate Technology

Magnetic exchange springs are composite structures that combine hard and soft (high and low magnetic anisotropy) materials to produce novel magnetic properties. Novel microwave frequency magnetization dynamics are obtained by modulating composition at the nanoscale.  Therefore exchange springs are one-dimensional electromagnetic metamaterials whose interaction with radiation is determined by artificial structure introduced at deep sub-wavelength length scales.  The exchange interaction is the strongest force in magnetism yet it remains essentially untapped in driving magnetization dynamics.  Optically induced unwinding of exchange springs harnesses the exchange interaction for the first time [1] and is the subject of an underpinning EPSRC grant award [2].  Initially an applied magnetic field will be used to wind springs in soft layers adjoined by hard layers with collinear magnetization so that the character of the magnetization precession within both hard and soft magnetic layers may be explored.  Rare earth - metal transition (RE-TE) Laves phase superlattices are ideal for this purpose due to their structural perfection and the large literature describing their static magnetic properties.  Focus will then shift to transition metal based structures that are of greater technological interest and in which hard layers with non-collinear magnetization will be sought so that an exchange spring exists within the soft layer even within the field-free state.  The project will then explore the assistance that the exchange interaction can give to optically induced magnetic switching, and the role of patterning at the nanoscale in stabilising coherent rotation of the magnetization.

Ultrafast and high frequency phenomena are of ever increasing importance in the development of information technology.  There are opportunities to apply underlying principles to new types of materials and devices, and to draw upon knowledge gained in other areas of science and technology. Therefore it is essential to remain aware of developments within neighbouring fields.  Membership of the CDT cohort and community will foster this awareness, while the skills training available within the CDT will provide a solid foundation for future employment.

[1] “Ultrafast optical parametric pumping of magnetization reorientation and precessional dynamics in DyFe2/YFe2exchange springs”, L. R. Shelford, Y. Liu, U. Al-Jarah, P. A. J. de Groot, R. C. C. Ward, and R. J. Hicken, Phys. Rev. Lett. 113, 067601 (2014).
[2] “Picosecond Dynamics of Magnetic Exchange Springs”, EPSRC EP/P008550/1.

This studentship is part of the Centre of Doctoral Training in Metamaterials. Please see all fully funded opportunities.

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